1. Field of the Invention
The present invention relates generally to antenna apparatuses and systems, and more particularly, to planar antennas with non-dispersive, ultra wide bandwidth (UWB) characteristics.
2. Discussion of the Background
With respect to the antenna of radar and communications systems, there are five principle characteristics relative to the size of the antenna: the radiated pattern in space versus frequency, the efficiency versus frequency, the input impedance versus frequency, and the dispersion. Typically, antennas operate only with a few percent bandwidth, and bandwidth is defined to be a contiguous band of frequencies in which the VSWR (voltage standing wave ratio) is below 2:1. In contrast, ultra wide bandwidth (UWB) antennas provide significantly greater bandwidth than the few percent found in conventional antennas, and exhibits low dispersion. For example, as discussed in Lee (U.S. Pat. No. 5,428,364) and McCorkle (U.S. Pat. Nos. 5,880,699, 5,606,331, and 5,523,767), UWB antennas can cover 5 or more octaves of bandwidth without dispersion. A discussion of other UWB antennas is found in xe2x80x9cUltra-Wideband Short-Pulse Electromagnetics,xe2x80x9d (ed. H. Bertoni, L. Carin, and L. Felsen), Plenum Press New York, 1993 (ISBN 0-306-44530-1).
As recognized by the present inventor, none of the above UWB antennas, however, provide high performance, non-dispersive characteristics in a cost-effective manner. That is, these antennas are expensive to manufacture and mass produce. The present inventor also has recognized that such conventional antennas do not permit integration of radio transmitting and/or receiving circuitry (e.g., switches, amplifiers, mixers, etc.), thereby causing losses and system ringing (as further described below).
Ultra wide bandwidth is a term of art applied to systems that occupy a bandwidth that is approximately equal to their center frequency (e.g., the bandwidth between the xe2x88x9210 dB points is 50% to 200%). A non-dispersive antenna (or general circuit) has a transfer function such that the derivative of phase with respect to frequency is a constant (i.e., it does not change versus frequency). In practice, this means that a received impulse E-field waveform is presented at the antenna""s output terminals as an impulse waveform, in contrast to a waveform that is spread in time because the phase of its Fourier components are allowed to be arbitrary (even though the power spectrum is maintained). Such antennas are useful in all radio frequency (RF) systems. Non-dispersive antennas have particular application in radio and radar systems that require high spatial resolution, and more particularly to those that cannot afford the costs associated with adding inverse filtering components to mitigate the dispersive phase distortion.
Another common problem as presently recognized by the inventor, is that most UWB antennas require baluns because their feed is balanced (i.e., differential). These baluns entail additional manufacturing cost to overcome, and cause poor performance. For example, the symmetry of the radiation pattern (e.g., azmuthal symmetry on a horizontally polarized antenna) associated with balanced antennas can be poor because of feed imbalances arising from imperfect baluns. Due to the limited response of ferrite materials, the balun, instead of the antenna, can limit the antenna system bandwidth. Inductive baluns, for example, are traditionally used and are both expensive, and bandwidth limiting.
Another problem with traditional UWB antennas is that it is difficult to control system ringing. Ringing is caused by energy flowing and bouncing back and forth in the transmission line that connects the antenna to the transmitter or receiverxe2x80x94like an echo. From a practical standpoint, this ringing problem is always present because the antenna impedance, and the transceiver impedance are never perfectly matched with the transmission line impedance. As a result, energy traveling either direction on the transmission line is partially reflected at the ends of the transmission line. The resulting back-and-forth echoes thereby degrade the performance of UWB systems. That is, a series of clean pulses of received energy that would otherwise be clearly received can become distorted as the signal is buried in a myriad of echoes. Ringing is particularly problematic when echoes from a high power transmitter obliterate the microwatt signals that must be received in radar and communication systems. The duration of the ringing is proportional to the product of the length of the transmission line, the reflection coefficient at the antenna, and the reflection coefficient at the transceiver. In addition to distortion caused by ringing, transmission lines can be dispersive, and always attenuate higher frequencies more than lower frequencies, causing distortion and stretching of the pulses flowing through the transmission line.
In view of the foregoing, there still exists a need in the art for a simple UWB antenna that can permits integration of electronics.
It is also an object of this invention to provide an all electronic means of generating and receiving balanced signals without costly, bandwidth limiting inductive baluns.
Another object of the present invention is to build array antennas with unique properties because each array element is separately powered (i.e., the ground and power for the active electronics circuit of each array element is decoupled from the other elements).
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that is inexpensive to mass-produce.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that has a flat magnitude response and flat phase response over ultra wide bandwidths.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that exhibits a symmetric radiation pattern.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that is efficient, yet electrically small.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that integrates transmission and reception circuits on the same substrate.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that is planer and conformal, so as to be capable of being easily attached to many objects.
It is a further object of this invention to provide a novel apparatus and system for providing a UWB antenna that can be arrayed in 1D (dimension), in which the array of UWB antennas are built on single substrate with the radiation directed in the plane of the substrate.
According to another aspect of the invention, an antenna device having Ultra Wide Bandwidth (UWB) characteristics comprises a first balance element coupled to a terminal at one end. A second balance element is coupled to another terminal at one end, the second balance element having a shape mirroring a shape of the first balance element to provide a symmetry plane between the first balance element and the second balance element, wherein each of the balance elements is made of a generally conductive material. A ground element is situated between the first balance element and the second balance element with an axis of symmetry on the symmetry plane. The above arrangement advantageously provides an UWB antenna that permits the placement of electronics within the antenna.
According to another aspect of the invention, an Ultra Wide Bandwidth (UWB) antenna system comprises a plurality of antenna elements. Each of the plurality of antenna elements includes a first balance element that is coupled to a terminal at one end, and a second balance element that is coupled to another terminal at one end. The second balance element has a shape that mirrors the shape of the first balance element, wherein each of the balance elements is made of a generally conductive material. Each of the antenna elements also includes a ground element that is situated between the first balance element and the second balance element. A timed splitter/combiner circuit is coupled to the plurality of antennas and is configured to steer a beam associated with the plurality of antennas. The above arrangement advantageously provides flexibility in the design of the antenna system, while maintaining cost-effectiveness.
According to yet another aspect of the invention, a method is provided for transmitting signals over an Ultra Wide Bandwidth (UWB) frequency spectrum. The method includes receiving an input source signal at a transmitter. The method also includes radiating a transmission signal at a plurality of terminals in response to the source signal using a UWB antenna. The UWB antenna includes a plurality of balance elements and a ground element that is disposed between the plurality of elements. The balance elements are coupled to terminals. The ground element houses the transmitter. One of the plurality of ground elements has a shape that mirrors another one of the plurality of ground elements. Each of the balance elements is made of a generally conductive material. Under this approach, a cost effective UWB antenna exhibits high performance.
According to yet another aspect of the invention, a method is provided for receiving signals over an Ultra Wide Bandwidth (UWB) frequency spectrum. The method includes a step of receiving the signals via a UWB antenna. The UWB antenna includes a plurality of balance elements and a ground element that is disposed between the plurality of elements. The balance elements are coupled to terminals. The ground element houses the transmitter. One of the plurality of ground elements has a shape that mirrors another one of the plurality of ground elements. Each of the balance elements is made of a generally conductive material. The method also includes outputting a differential signal based upon the receiving step. Under this approach, a UWB antenna provides integration of electronics, thereby minimizing transmission line losses and system ringing.
According to another aspect of the invention, an Ultra Wide Bandwidth (UWB) antenna system comprises a plurality of array elements that are arranged in 1D (dimension). Each of the plurality of array elements includes a first balance element that is coupled to a terminal at one end, and a second balance element that is coupled to another terminal at one end. The second balance element has a shape that mirrors the shape of the first balance element to provide a symmetry plane between the first balance element and the second balance element, wherein each of the balance elements is made of a generally conductive material. Each of the antenna elements also includes a ground element that is situated between the first balance element and the second balance element with an axis of symmetry on the symmetry plane. A timed splitter/combiner circuit is coupled to the plurality of array elements and is configured to control the plurality of array elements. The above arrangement advantageously provides flexibility in the design of the antenna system.
With these and other objects, advantages and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings herein.